30-Second HTTPS Crypto Cracking Tool Released

Three researchers who discovered a crypto attack that can be used to grab sensitive information from HTTPS traffic in less than 30 seconds have released a tool to help website operators see if their systems are susceptible.

Their presentation triggered a Department of Homeland Security warning that "a sophisticated attacker may be able to derive plaintext secrets from the ciphertext in an HTTPS stream," and that all versions of the transport layer security (TLS) and secure sockets layer (SSL) protocols are vulnerable.

The man-in-the-middle HTTPS crypto attack involves watching "the size of the cipher text received by the browser while triggering a number of strategically crafted requests to a target site," according to exploit details that the developers shared with DHS. "To recover a particular secret in an HTTPS response body, the attacker guesses character by character, sending a pair of requests for each guess. The correct guess will result in a smaller HTTPS response," said the DHS.

Prado has previously said that crafting a fix for HTTPS itself will be a "nontrivial" undertaking.

In the meantime, he and his fellow researchers this week released a tool for launching a BREACH attack for testing purposes. Their tool is available both in the form of source code and instructions, as well as a precompiled binary.

"This is intended for self-assessment only," according to the BREACH tool download page. "Don't do bad things."

To use the tool, "you will need a Windows computer or [virtual machine] to build and run the tool," Prado said in an email interview. Other requirements include the .NET 3.5+ Framework and Visual Studio 2010 or newer, for anyone who wants to modify the code, which is being hosted on GitHub. The tool has been tested with Windows 7.

When using the tool, no man-in-the-middle attack is required for testing a site. Instead, the developers recommended simply pointing the tool -- which emulates a Web client -- at encrypted HTTPS traffic, using a hosts file, which allows host names to be associated with IP addresses.

In addition to this "simple HTTP client that simulates browser behavior," the researchers promised they would release a more full-fledged, browser-based tool that website operators can use to test their susceptibility to a BREACH attack.

Tough to say, but when DHS issues an alert, the risk isn't zero. Likely, this vulnerability could be built on by attackers in the future, so that when paired with an intrusion, they'd be able to siphon away intercepted HTTPS data, which -- because it's being sent using HTTPS -- is more likely to contain sensitive information. So this is more like a warning of dangers to come, unless fixes get made.

Excellent question, I should have referred to previous reporting that included that answer: The researchers have outlined a number of mitigation possibilities, such as separating secrets from user input, or masking secrets by making them random.

These are fixes that would likely need to be implemented by website server software developers, meaning it's not going to happen immediately, either on the development or subsequent implementation front.

One caveat with the vulnerability is that an attacker would first need to infiltrate a target network to then begin sniffing traffic.

Published: 2015-03-31The build_index_from_tree function in index.py in Dulwich before 0.9.9 allows remote attackers to execute arbitrary code via a commit with a directory path starting with .git/, which is not properly handled when checking out a working tree.